Theproposed study will investigate the physiologic role of catecholamines in the developing fetus. By virtue of their effects of the cardiovascular system and general metabolism, catecholamines are known to be important in the mature animal's response to various physiologic or pathologic alterations in its environment. We will study the role of the sympathoadrenal system in fetal cardiovascular and metabolic homeostasis. In particular we will quantitate the secretion of circulating epinephrine and norepinephrine in the chronically instrumented fetal lamb under basal conditions and during hypoxic stress. The role of circulating catecholamines in the fetal cardiodynamic response to hypoxemia will be studied as well as the interrelationship of hyperglycemia and sympathoadrenal function during adaption to hypoxemia. Epinephrine and norepinephrine will be measured using a sensitive and specific radioenzymatic assay. This work will contribute to a fundamental gap in our knowledge of fetal physiology, and also provide information of clinical importance.